Given the pivotal role of anti-apoptotic Bcl-2 family proteins in cancer cell survival, development of anti-cancer therapeutics targeting the BH3 binding groove of anti-apoptotic Bcl-2 proteins has emerged as a promising, but difficult goal. Initial compounds targeted to the structure of Bcl-xL, and thereby able to bind to Bcl-2, Bcl-xL and Bcl-W, have shown promise in the clinic for the treatment of cancer, though studies have discovered that Mcl-1 over-expression allows cancers to evade treatment. To this end, the recent success with stable and cell permeable stapled BH3 peptides targeting Bcl-2 has provided the impetus to identify peptide sequences capable of selectively binding to Mcl-1 which is one major Aim of this proposal. If successful, our studies could result in advanced clinical candidates for the treatment of cancer. To test our hypotheses we will characterize and further determine the structural basis for inhibition, and subsequently we will test the potential anti-cancer activity of the proposed compounds in advanced pharmacological studies in cell and mice models of prostate cancer.